The investigation of renal hypertension in pregnant sheep will progress along two lines. First, the cardiac output and blood volume will be recorded from 80 gestational days until term (140 days). The animals will be placed in three groups: 1) Control, to determine normal changes during pregnancy, 2) two kidney renal hypertension, 3) one kidney hypertension. Cardiac output will be monitored by an implanted electromagnetic flow probe around the pulmonary artery and blood volume by an isotope dilution method. The second area of investigation will be to determine the effects of hypertension upon fetal umbilical blood flow and oxygen consumption. Using a chronic sheep model, fetuses will be instrumented for determination of umbilical blood flow by electromagnetic flow transducers and umbilical venous and arterial catheters placed. BIBLIOGRAPHIC REFERENCES: Nuwayhid, B., Brinkman, C.R. III, Su, C., Beven, J.A., and Assali, N.S.: Development of autonomic control of fetal circulation. Am. J. Physiol. 228:337, 1975. Brinkman, C.R. III, Nuwayhid, B. and Assali, N.S.: Renal hypertension and pregnancy in the sheep. I. Behavior of uteroplacental vasomotor tone during mild hypertension. Am. J. Obstet. Gynecol., 121:931-937, 1975.